find objects with bounding boxes - opencv

Question

I would like to find bounding boxes for each object in the picture and after I found that, I crop out the bounding boxes and use it for the next steps.Here is the input picture after preprocessing.
I have a code for bounding box, but it just works well for 1 object. If there are 2 objects it sums up both and draw a bounding box around both of them. Here is the first output. The code for it is:
vector<vector<Point>> contours;
vector<Point> points;
findContours(erod, contours, CV_RETR_LIST, CV_CHAIN_APPROX_NONE);
for (size_t i = 0; i < contours.size(); i++) {
for (size_t j = 0; j < contours[i].size(); j++) {
Point p = contours[i][j];
points.push_back(p);
}
}
if (points.size() > 0) {
Rect brect = boundingRect(Mat(points).reshape(2));
cv::rectangle(erod, brect.tl(), brect.br(), Scalar(100,100,200), 2, CV_AA);
Mat ROI = frame(brect);
}
The secound thing I tried was using the code of the documentation of OpenCV. Here I changed CV_RETR_TREE in findContours to CV_RETR_EXTERNAL but I still get to many bounding boxes and I don't know how to crop out the boxes.
Thanks a lot!

Answer 1

Before finding contours you should do some morphological opening to clear all the noise and lines:
Mat morphKernelOpen = Imgproc.getStructuringElement(Imgproc.MORPH_RECT, new org.opencv.core.Size(20, 20));
Imgproc.morphologyEx(mat, mat, Imgproc.MORPH_OPEN, morphKernelOpen);
Result:
Also, there are some black spaces inside your objects, so to avoid finding contours in them, your findContours function should be under CV_RETR_EXTERNAL mode:
Imgproc.findContours(scharrThresh, scharrThreshContours, new Mat(), Imgproc.RETR_EXTERNAL, Imgproc.CHAIN_APPROX_SIMPLE);
In the end you'll have two contours and you can continue your boxes finding as you did previously
If you do not like soft edges around your objects you can do threshold function before morphological opening. Getting 100% accurate contours around your objects would be very hard or nearly impossible due to too much noise in the image. Also, if you can, next time if you ask put the result image you get after the actions you do, it will be easier to give you a proper answer.